It’s been almost a month since Apple rolled out the latest iOS update. Existing Apple i-device owners are enjoying the new update along with more than four million people who recently purchased the iPhone 4S. The updated version of the operating system brings more than 200 new features to the table. For the millions of people now using iOS 5, here is a guide to its most useful new features:

Siri

Easily the most significant addition to iOS 5 is Siri, the new personal assistant currently only available on the iPhone 4S. Siri has has everyone from sci-fi fans to master’s degree students excited that Apple’s made the first step toward the talking computers we’ve dreamed of for decades. This voice recognition software “listens” to what the user says and performs a nearly unlimited range of tasks. Among other things, Siri can play music, set alarms, look up calendar events, and check the weather. The service can be activated by holding down the Home button or just bringing the iPhone up to one’s ear.

Notification Center

The new Notification Center has also fundamentally changed the way users interact with iOS. By swiping down from the top of the screen anywhere in iOS 5, users can view all of their notifications. Text messages, e-mails, and anything else that generates a notification can all be found and dealt with here. Notifications also show up on the lock screen now, eliminating the need to unlock the phone to find out what that last beep was about.

Camera

Another aspect Apple spent a lot of time perfecting was the camera. The camera app has been upgraded so much that the hardware on the iPhone 4S is able to take pictures faster than nearly any other smartphone. There are also a number of other camera enhancements in iOS 5 not exclusive to the iPhone 4S. For starters, there’s now a camera button on the lock screen. Also, once in the app, there’s a single tap focus option, after which pictures can be taken by using the volume-up button.

After a photo is taken, a new iCloud service called Photo Stream can be used to share the photo instantly to all of the user’s other iOS devices.

Twitter

Apple has built Twitter integration right into the framework of iOS so it’s accessible from a number of different stock apps, as well as future third-party programs. The most significant example of this tight integration is seen in that contacts and their Twitter handles are now linked, so iOS 5 users can start typing a contacts’ names and have the option to tweet them.

iCloud

One of Apple’s goals with iOS 5 was to let users’ devices communicate more easily. This is evident in the company’s free iCloud service. When enabled, it synchs all users’ files over all their devices. The service primarily targets music and photos, but it also works for documents and virtually any other files.

The iCloud service is great for synching iOS devices, but it doesn’t account for conventional computers running OS X. Fortunately, Apple has introduced WiFi Sync, an easy, automated synching method for iOS and OS X devices. When users purchase something on iTunes, be it a song, TV show, or anything else, it will automatically synch to other devices once they’re on the same network. Thanks to WiFi Sync, the days of purchasing something on a MacBook and having to manually transfer it to an iPod or iPhone are over.

Reminders

Reminders in iOS 5 aren’t a brand new concept, but they are a great development of an existing idea. While iCal is perfect for scheduling important events, reminders work well for smaller tasks. Reminders let users make short memos for themselves so they don’t forget to take care of the little things.

iMessage

One of the completely new features in iOS 5 is iMessage. For years, BlackBerry fans have touted the company’s BlackBerry Messenger. Apple’s new iMessage service is similar, allowing users of iOS 5 to send text messages to one another for free. Apple improves on the idea by building iMessage into the Messages app, so users still go to one place for all of their text messaging needs.

Newsstand

Apple has also made it easier to maintain digital subscriptions. Newsstand automatically refreshes magazine and newspaper subscriptions and gives users a portal to jump straight to their favorite publications. It even provides notifications for new updates.

Keyboard

One final noteworthy improvement are adjustments to the iOS keyboard. The keyboard now supports a sort of shorthand for users to type faster. Through an option in the Settings menu, users can set up ways to type short phrases and have the keyboard automatically fill in the rest. For example, a user could set the keyboard up to automatically type “talk to you later” when they type “ttyl.”

Between all of the new features Apple has packed into iOS 5, the company has made the operating system more efficient and friendlier to power users. At the same time, it’s kept its intuitiveness and remains easy for anyone to use. For this, iOS 5 has so far shown itself to be the strongest iOS update yet.